A flat-panel display is a matrix-addressed flat-panel device typically formed with a baseplate structure and a faceplate structure situated opposite the baseplate structure. In a flat-panel CRT display of the gated field-emission type ("field-emission display"), the baseplate structure contains a generally flat baseplate, a lower level of generally parallel emitter electrodes extending over the interior surface of the baseplate, a dielectric layer overlying the emitter electrodes, and an upper level of control (or gate) electrodes extending over the dielectric layer generally perpendicular to the emitter electrodes. Electron-emissive elements are situated in cavities in the dielectric layer and are exposed through openings in the control electrodes.
During operation of the field-emission display ("FED"), electrons emitted from selected electron-emissive elements move towards the faceplate structure. The electrons strike corresponding light-emissive regions in the faceplate structure and cause them to emit light that produces an image on the exterior surface of a transparent faceplate. Each of the locations at which one of the control electrodes crosses one of the emitter electrodes in the baseplate structure defines a picture element ("pixel") in a black and white display and a sub-pixel in a color display, three sub-pixels normally forming a color pixel.
Various types of equipment and procedures are employed in testing flat-panel displays to determine how much, if any, current flows in particular parts of the displays. It is generally desirable that testing for current flow be performed rapidly.
Henley, U.S. Pat. No. 5,073,754, describes how a liquid-crystal display ("LCD") is tested for short circuit defects, and thus for undesirable current flow, utilizing a magnetic sensor of undisclosed configuration. The magnitude of short circuit current increases with the magnitude of the sensed magnetic field. Henley's short circuit detection technique entails scanning the magnetic sensor across parts of the LCD, thereby enabling currents that characterize short circuit defects to be identified quickly. Consequently, magnetic sensing is a promising way of assessing current flow. It is desirable to have equipment that utilizes magnetic sensing in producing data indicative of current flow in flat-panel displays, especially FEDs.